It is important to suppress deterioration in product quality and manufacturing yield in the manufacturing process of a semiconductor substrate, thin film substrate, etc. (hereinafter collectively referred to as an “inspection object”). During such a manufacturing process, dust generation around the manufacturing equipment and cleanness of the manufacturing process are monitored by detecting and managing foreign substances, flaws, defects, dirt, etc. (hereinafter collectively referred to as “foreign objects”) on the surface of the inspection object.
Examples of an apparatus for detecting foreign objects on the surface of an inspection object include surface inspection apparatuses as described in Patent Literatures 1 and 2. Such a surface inspection apparatus illuminates the surface of the inspection object with inspection light at a fixed position, and moves (translates) the illuminated inspection object in a direction while the object is rotated. With this operation, the surface of the inspection object is spirally scanned with the area illuminated with the inspection light (hereinafter referred to as an “illumination spot”). By detecting scattered light generated at the surface of the substrate to be inspected surface, the inspection apparatus detects a foreign object existing on the surface of the inspection object or in a part of the inspection object in the vicinity of the surface. It is to be noted that a “main scan” means a scan in the direction of the rotation of the inspection object while an “auxiliary scan” means a scan in a direction orthogonal to the main scan.
An apparatus disclosed in Patent Literature 3 is designed to be capable of changing the diameter of the illumination spot (measured in the main scan direction) on the inspection object. The illumination spot's diameter in the main scan direction is changed such that the diameter increases as the illumination spot approaches the rotation center of the inspection object (decreases as the illumination spot moves away from the rotation center). By the control of the illumination spot's diameter, the surface temperature rise of the inspection object and the detection sensitivity to foreign substances/defects are maintained substantially constant during the inspection. Meanwhile, Patent Literatures 4 and 5 have disclosed a technique in which multiple illumination spots with fixed diameters are formed on the surface of the inspection object and scattered light from the illumination spots is detected.